Biochemistry
6th Edition
ISBN: 9781305577206
Author: Reginald H. Garrett, Charles M. Grisham
Publisher: Cengage Learning
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Chapter 20, Problem 3P
Interpretation Introduction
To propose:
From the given, the equation is suggested that gives the pH dependence and also calculating the pH8 reaction’s reduction potential.
Introduction:
In the
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Standard redox potentials Eo' for some common compounds in biochemistry:
Eo' (Volt)
+ 0,81
+0,42
+ 0,25
12 O₂ + 2 H+ + 2 e
NO3 + 2 H+ + 2 e
2 cyt c (ox) + 2 e
2 cyt b (ox) + 2 e
Pyruvate + 2 H+ + 2 e*
NAD + 2 H+ + 2 e
Acétoacétate + 2 H+ + 2 e
(2) acétoacétate + NADH + H+
H₂O
NO₂ + H₂O
2 cyt c (red)
2 cyt b (red)
Lactate
(3) 2 cyt c (ox) + 2 cyt b (red)
NADH + H+
B-hydroxybutyrate
+ 0,08
- 0,19
With the help of the above table, determine the spontaneous direction of the following
reactions in the standard conditions. Justify your answers by calculating the Gibbs
(free) energy of reaction in each case.
(1) pyruvate + ß-hydroxybutyrate
-0,32
- 0,35
lactate + acétoacétate
B-hydroxybutyrate + NAD+
2 cyt c (red) + 2 cyt b (ox)
Begining with 1 M concentrations of each reactant and product at pH=7 and 25.0 degrees C, calculate the K'eq of the reaction Pyruvate
+ NADH Lactate + NADH+H+.
Note the temperature of this reaction will not affect the standard reducton potential delta E° in the table 13-7b.
9. TCA cycle and electromotive force-Consider the following reaction:
malate + NAD 32>oxaloacetate + NADH
The free energy for this reaction depends on the [NAD]/[NADH] ratio and the [malate]/[oxaloacetate]
ratio, with AGO' = 30 kJ/mol, AG° is simply AG°at pH 7.
a) Assuming that the [malate]/[oxaloacetate] ratio is fixed at 10, generate a plot of AG versus
[NAD]/[NADH].
b) Assuming that the [malate]/[oxaloacetate] ratio is still fixed at 10, in which direction will this portion
of the TCA cycle run for [NAD]/[NADH] = 1?10?100?
c) For [NAD+] = 10 mM and [NADH] = 0.1 mM, and the [malate]/[oxaloacetate] ratio still fixed at 10,
what is AG for the above reaction?
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